BINDER TYPE SELECTION FOR FOAMED COLD MIX ASPHALT
Abstract
As a road material, foamed cold mix asphalt (FCMA) is a unique mixture since the formation of bitumen- aggregate bonds is different from that of other common bituminous mixtures. In the mixing process, the binder is sprayed in the form of foam onto wet aggregates in which its quality is affected by many factors included binder properties. It is reasonable to assume that the binder type play an important role in mix performance. This investigation was designed to explore the way in selecting binder type for FCMA. Three binder types, i.e. pen 50/70, pen 70/100, and pen 160/220, and crushed virgin limestone aggregate were selected for the production of FCMA specimens in the laboratory. The foam produced at varies bitumen temperature was mixed with the aggregate at different mixing protocol. The resulting asphalt mixtures were then compacted using a Gyratory compactor to produce specimens with diameter of 100mm. All specimens were finally tested using Indirect Tensile Stiffness Modulus in order to evaluate their performance. Overall, when selecting binder type for FCMA material three things should be considered, i.e. bitumen temperature, mixer capability, and regional climate. It is suggested that high temperature (160oC to 180oC) is applied for low bitumen pen (pen 50/70), and low temperature (140oC to 160oC) for high bitumen pen (pen 160/220). A FCMA using low bitumen pen should be mixed using a high speed mixer to ensure good binder distribution; if a suitable mixer is not available, it is better to use a higher bitumen pen. If a FCMA is to be paved in a cold region, a softer binder will be better since binder distribution is more important in developing mixture stiffness at low temperature; however in a hot region, a harder binder is more suitable since binder modulus is more important in developing mixture stiffness at high temperature.